1. Field of the Invention
The present invention relates to an ink jet recording head which can discharge an ink drop onto a recording medium corresponding to image information for recording, a driving condition setting method thereof, and an ink jet recording device.
2. Description of the Related Art
As an ink jet recording method which can discharge an ink drop from a nozzle onto paper corresponding to an image signal for recording, there is a thermal ink jet method including the steps of: applying an electric pulse, as a driving force for discharging an ink drop from a nozzle, to an electrothermal conversion element (hereinafter, referred to as heating element); producing a bubble by heat generation of a heating element; and discharging an ink drop from the nozzle by pressure of the bubble.
The thermal ink jet method has the problem that the ink temperature is raised by discharge of an ink drop so that the volume of the ink drop is varied due to viscosity change.
To solve this, as shown in U.S. Pat. No. 2,783,647 (hereinafter, referred to as a Related Art 1), there is proposed an ink jet recording method in which a bubble produced on a heating element grows to be communicated to atmosphere so as to discharge an ink drop having a constant volume irrespective of environment temperature and head temperature. This will not allow a bubble to disappear on the heating element. Therefore no cavitation damage when a bubble disappears can be given to the heating element. The life of the heating element can be increased.
The Related Art 1 also discloses that, in order to prevent image contamination due to splash or mist produced when a bubble is communicated to atmosphere, a bubble is communicated to atmosphere on condition that the internal pressure of the bubble is lower than the atmospheric pressure.
Ink mist is attached onto paper because a bubble is communicated to atmosphere before the internal pressure of the bubble produced by driving a heating element is lower than the atmospheric pressure, whereby a pressure gradient is produced from a nozzle to atmosphere. A bubble is communicated to atmosphere after the internal pressure of the bubble is lower than the atmospheric pressure to provide a pressure gradient toward the inside of a nozzle, whereby ink mist is prevented from being attached onto paper.
To achieve the abovementioned relation, the relation between timing for communicating atmosphere and a bubble to each other and a channel volume from a heating element to a nozzle will be described with reference to FIG. 13 showing typical change of bubble internal pressure with time.
FIG. 13 shows results of head constructions a, b and c which change a distance from a heating element to a nozzle to vary a channel volume in which the driving condition (bubble volume produced) of a heating element is constant to calculate timing for communicating a bubble to atmosphere by a fluid simulation. Here, when the respective channel volumes are Va, Vb and Vc, the relation is Va less than Vb less than Vc.
As shown in FIG. 13, in the construction a in which a channel volume from a heating element to a nozzle is too small, a bubble is communicated to atmosphere (the bubble internal pressure is higher than the atmospheric pressure) before time t1 at which the bubble internal pressure and the atmospheric pressure are equal to each other, whereby ink mist is attached onto paper. In the construction c in which a channel volume from a heating element to a nozzle is too large, a bubble is not communicated to atmosphere, whereby the abovementioned effect for discharging an ink drop having a constant volume irrespective of temperature and for increasing the life of the heating element cannot be obtained.
The relation between a channel volume from a heating element to a nozzle and a driving condition of the heating element (the volume of a bubble produced by the heating element) governs timing for communicating atmosphere and a bubble to each other.
From such a point of view, U.S. Pat. No. 2,877,589 (hereinafter, referred to as a Related Art 2) discloses that the size of a heating element and a channel volume to a nozzle are defined within a certain range.
The Related Arts 1 and 2 each disclose a construction which can prevent ink mist contamination and discharge an ink drop having a constant volume irrespective of temperature.
It is difficult, however, to produce a channel volume within a certain range due to a production error of an ink jet recording head. In the production process of an ink jet recording head (head chip), the following factors which fluctuate a channel volume from a heating element to a nozzle can be considered.
For example, in an ink jet recording head in which a nozzle plate is stuck onto a member formed with an ink channel to form a nozzle in the nozzle plate, the thickness of the nozzle plate may not be a desired thickness and, when forming a nozzle, a nozzle of a desired size may not be formed.
In addition, in an ink jet recording head in which a channel substrate formed with a channel and a heating element substrate formed with a heating element are joined together so as to form a nozzle surface by dicing, the dicing position may be displaced.
In such a case, the channel volume from a heating element to a nozzle is outside the defined range. As in the Related Arts 1 and 2, atmosphere and a bubble cannot be communicated to each other at a predetermined timing, so that desired operations (discharge of an ink drop having a constant volume and prevention of ink mist contamination) cannot be achieved.
However, when the allowed volume of a channel size is strictly defined in order to allow a bubble volume and a channel volume to be in a predetermined relation, the yield of the ink jet recording head in the head production process can be lowered and the production cost can be increased.
The present invention has been made in view of the above circumstances and provides a driving condition setting method of an ink jet recording head, an ink jet recording head, and an ink jet recording device, which can ensure desired printing performance irrespective of fluctuation of the channel volume for each head chip.
According to the present invention, a driving condition setting method of an ink jet recording head having an individual channel in which a heating element is placed for heating ink to produce a bubble and an ink discharge portion at an edge of the individual channel, includes the step of setting a driving condition of the heating element corresponding to a difference in a channel volume of the individual channel from the heating element to the ink discharge portion due to a production error.
In this manner, a driving condition applied to a heating element corresponding to a difference in a channel volume of an individual channel from the heating element to the ink discharge portion is set. Specifically, in the ink jet recording head production process, when a channel volume from the heating element to the ink discharge portion is displaced from a predetermined value, the condition to drive a heating element is changed corresponding to the displacement amount to vary the volume of a bubble produced by the heating element. The channel volume from the heating element to the nozzle and the bubble volume are allowed to be in a predetermined relation. For example, when a channel volume is small, energy to applied to the heating element is lowered to decrease the volume of a bubble produced in ink. When a channel volume is large, energy to be applied to the heating element is raised to increase the volume of a bubble produced in ink.
The bubble volume and the channel volume are allowed to be in a predetermined relation. When ink is discharged, a bubble can be communicated to atmosphere at any time at the internal pressure of the bubble lower than the atmospheric pressure. Therefore, an ink drop having a constant volume can be discharged irrespective of environment temperature and head temperature, and image deterioration due to splash or mist can be prevented.
An ink jet recording head of the present invention includes: an individual channel in which a heating element is placed for heating ink to produce a bubble; an ink discharge portion at an edge of the individual channel; and a data holding unit for storing channel volume data based on a channel volume of the individual channel from the heating element to the ink discharge portion.
The ink jet recording head is provided with a data holding unit for storing channel volume data. Therefore, even when the production accuracy of the ink jet recording head is low, a driving condition of a heating element is set based on the channel volume data so as to allow the channel volume and the bubble volume to be in a predetermined relation. The ink jet recording head which can suppress the volume fluctuation of an ink drop with temperature change and achieve prevention of ink mist contamination can be obtained without lowering the yield.
An ink jet recording device of the present invention includes a driving condition setting part which reads channel volume data of the recording head to set a driving condition of the heating element by mounting the ink jet recording head according to one aspect of the present invention.
The abovementioned ink jet recording head is mounted to read the channel volume data of the ink jet recording head and set a driving condition of a heating element according to the data. Therefore, the bubble size and the channel volume of the ink jet recording head are allowed to be in a predetermined relation, and prevention of ink mist contamination and a constant ink drop volume can be achieved.
In the ink jet recording head, a position of the heating element is set so that a bubble produced on the heating element grows to be communicated to atmosphere, thereby discharging an ink drop.
In the ink jet recording head, a unique driving condition data corresponding to head chip dicing displacement due to a production error is held for each head chip.